Zoom lens barrel assembly

ABSTRACT

A zoom lens barrel assembly includes a plurality of lens barrels including a rearmost lens barrel, secured to a camera body, and a frontmost lens barrel. At least one adjacent pair of lens barrels are connected to each other via a helicoid structure. The frontmost lens barrel and a first adjacent lens barrel are connected to each other via a cam structure. The helicoid structure allows the adjacent pair of the lens barrels to rotate and move in an optical axis direction relative to each other while the zoom lens barrel assembly moves from a retracted position to a minimally extended position for a photographing operation. At least a portion of the helicoid structure includes a slip region which allows the pair of adjacent lens barrels to rotate without relatively moving along the optical axis.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a zoom lens barrel assembly, and inparticular, to a multi-stage-extension zoom lens barrel assembly havinga lens barrier.

2. Description of the Related Art

There are concurrent needs to increase magnification of camera zoomlenses and to miniaturize them. For this reason, modern zoom lenses areconstructed as a multi-stage-extension zoom lens barrel assembly. Amulti-stage-extension zoom lens barrel assembly employs a helicoidstructure or a cam structure to connect barrels and allow them to moverelative to one another. Although the cam structure permits a highdegree of freedom in terms of how much a lens barrel can extend outwardsfor a predetermined rotation angle of the barrel, it is difficult toensure rigidity and light-blocking performance of the lens barrel withthis structure. However, the helicoid structure ensures rigidity andlight-blocking performance of the lens barrel although this structureallows the lens barrel to extend outward only by a fixed amount for apredetermined rotation angle of the barrel. For this reason, thehelicoid structure is considered more suitable for use in multi-stageextension lens barrel assemblies.

A typical zoom lens barrel assembly includes a lens barrier on thefrontmost end thereof. This lens barrier is opened and closed by makinguse of relative movement between the frontmost barrel having the lensbarrier and an adjacent barrel. When there are many stages (sub-barrels)in a barrel assembly, however, the relative displacement between thelens barrels may become too small to provide sufficient stroke lengthrequired for the opening/closing of the lens barrier. In particular, inthe case of a wide-angle zoom lens, in which the optical system has asmall length at the wide-angle extremity, displacement of the lensbarrel assembly from its retracted position, where the length of thebarrel assembly and thus the length of the optical system are smallest,to the wide-angle extremity is small. If helicoid structures are used insuch a zoom lens barrel assembly, leads of the helicoids of each barrelneed to be close to each other in order to effectively make use of thelength of the zoom lens barrel. This makes displacement of each lensbarrel substantially equal to one another. As a result, sufficientstroke length required for the opening/closing of the lens barriercannot be achieved.

To cope with above problems, only the frontmost lens barrel isconstructed to have a cam structure so that the frontmost lens barrelextends outward by a larger amount for a small rotation angle and causesthe other lens barrels to extend only by a small amount. Whilesufficient stroke can be achieved, the lead for advancing the frontmostlens barrel to open the lens barrier becomes too large. This can causetoo large a resistance when the lens barrel is retreated, which affectsthe strength of the lens barrel. In addition, if only the frontmost lensbarrel extends outward by a large amount, tension is undesirable exertedon a flexible printed board, which connects a shutter unit mounted onthe frontmost lens barrel to a circuit board in a camera body.

As an alternative approach, the other lens barrels that are connected tothe frontmost lens barrel can be each constructed to have a camstructure in order to provide a section or sections that allow the zoomlens barrel to extend outward only by a small amount, or do not extendoutward at all, when the barrels are rotated. In this construction, thesufficient stroke length for the opening/closing of the lens barrier isprovided within a rotation range between the retracted position and thewide-angle extremity. Such cam structures, however, make it difficult toensure sufficient rigidity of the zoom lens barrel assembly. It shouldbe noted that the rearmost lens barrel cannot be constructed as a camstructure since the driving force needs to be transmitted through gearsto the first lens barrel.

SUMMARY OF THE INVENTION

In view of the above-described drawbacks of the conventional lens barrelassemblies, the present invention provides a novel zoom lens barrelassembly structure that not only enhances the rigidity ofmulti-stage-extension zoom lens barrel, but also provides a sufficientstroke length needed for the opening/closing of a lens barrier.

For example, a zoom lens barrel assembly is provided, including aplurality of lens barrels including a rearmost lens barrel, secured to acamera body, and a frontmost lens barrel. At least two adjacent lensbarrels, of the plurality of lens barrels arranged between the camerabody and the frontmost lens barrel, are connected to each other via ahelicoid structure. The frontmost lens barrel and a first adjacent lensbarrel are connected to each other via a cam structure. The helicoidstructure allows the at least two adjacent lens barrels to rotate andmove in an optical axis direction relative to each other while the zoomlens barrel assembly moves from a retracted position to a minimallyextended position for a photographing operation. At least a portion ofthe helicoid structure includes a slip region which allows the at leasttwo adjacent lens barrels to rotate without relatively moving along theoptical axis.

A barrier mechanism can be provided on the frontmost lens barrel, thebarrier mechanism being opened and closed via movement of the frontmostlens barrel in the optical axis direction as the zoom lens barrelassembly moves between the retracted position and the minimally extendedposition, and by relative rotation of the at least two adjacent lensbarrels via the slip region.

It is desirable for the first adjacent lens barrel connected to thefrontmost lens barrel via the cam structure to be connected to a secondadjacent lens barrel via a second helicoid structure which causes theconnected the first and second adjacent lens barrels to rotate and movealong the optical axis relative to each other as the zoom lens barrelassembly moves from the retracted position to the minimally extendedposition, the second helicoid structure also including a slip regionwhich allows the first adjacent lens barrel and the second adjacent lensbarrel to rotate without relatively moving along the optical axis.

In another embodiment, a four-stage-extension zoom lens barrel isprovided, including a first barrel connected to a fixed barrel securedto a camera body, the first barrel being movable so as to retreat andadvance relative to the fixed barrel; a second barrel connected to thefirst barrel; a third barrel connected to the second barrel; a frontmostfourth barrel connected to the third barrel; wherein the first, second,and third barrels are each supported, and are movable in an optical axisdirection, via a helicoid structure. The frontmost fourth barrel and thethird barrel are connected to each other by a cam structure so as to bemovable in an optical axis direction. A barrier mechanism is provided onthe frontmost fourth barrel. The helicoid structures for moving thesecond barrel and the third barrel in the optical axis direction eachallow the second and the third barrels to rotate and relatively move inthe optical axis direction as the zoom lens barrel moves between aretracted position and a minimally extended position for a photographingoperation, each the helicoid structure having a slip region which allowsthe second and third barrels to rotate without relatively moving in theoptical axis direction. The barrier mechanism is opened and closed by arelative movement of the third barrel and the frontmost fourth barrel inthe optical axis direction as the slip sections allow the second and thethird barrels to rotate.

It is desirable for the fourth barrel to be connected to the thirdbarrel via the cam structure so that the fourth barrel moves in theoptical axis direction relative to the third barrel without rotating,and the barrier mechanism to be opened and closed by the relativemovement of the third barrel and the fourth barrel in the optical axisdirection in the slip section of the third barrel.

It is desirable for the slip section of the helicoid structure of thesecond barrel to have a different slip angle than the slip section ofthe helicoid structure of the third barrel.

The helicoid structure having the slip section can include a femalehelicoid formed on one of two adjacent barrels of the first throughthird barrels and a male helicoid formed on the other of the twoadjacent barrels, and the female helicoid can include a helicoid slipregion that permits rotation of the male helicoid when the two adjacentbarrels are in a retracted position.

In another embodiment, a zoom lens barrel assembly is provided,including a plurality of lens barrels including a rearmost lens barrelsecured to a camera body, and a frontmost lens barrel. The frontmostlens barrel and a first adjacent lens barrel are connected to each othervia a cam structure. The first adjacent lens barrel is connected to asecond adjacent lens barrel via a helicoid structure so that the firstand second adjacent lens barrels relatively rotate and relatively movein the optical axis direction as the zoom lens barrel assembly movesbetween a retracted position and a minimally extended position for aphotographing operation, the helicoid structure including a helicoidslip region which allows the first and second adjacent lens barrels torelatively rotate without relatively moving along the optical axis. Thehelicoid structure having the helicoid slip region includes a femalehelicoid formed on one of the first and second adjacent lens barrels anda male helicoid formed on the other of the first and second adjacentlens barrels. The female helicoid includes a helicoid slip region whichpermits rotation of the male helicoid when the first and second adjacentlens barrels are in the retracted position. A circumferential groove isformed along each of opposing thrust surfaces of the helicoid slipregion.

The helicoid structure having the helicoid slip region and thecircumferential groove can constitute a helicoid ring, the helicoid ringbeing formed by injection-molding a plastic material into a mold.

In another embodiment, a zoom lens barrel assembly is provided,including a pair of lens barrels connected to each other via a helicoidstructure, the helicoid structure including a helicoid slip region whichallows the pair of the lens barrels to relatively rotate withoutrelatively moving along the optical axis. The helicoid structure havingthe helicoid slip region includes a female helicoid formed on one of thepair of lens barrels and a male helicoid formed on the other of the pairof lens barrels. The female helicoid includes the helicoid slip regionwhich allows rotation of the male helicoid when the pair of lens barrelsare in a predetermined position. A circumferential groove is formedalong each of opposing thrust surfaces of the helicoid slip region ofthe female helicoid.

In another embodiment, a zoom lens barrel assembly is provided,including a plurality of lens barrels, at least two lens barrel of theplurality of lens barrels including a helicoid structure for allowingone lens barrel of the at least two lens barrels to rotate and extendand retreat as the zoom lens barrel assembly moves from a retractedposition to a minimally extended position for a photographing operation.The helicoid structure includes a helicoid slip section for allowing theone lens barrel to rotate without relatively moving along the opticalaxis, the helicoid structure including a female helicoid formed on oneof the at least two lens barrels and a male helicoid formed on the otherof the at least two lens barrels, the male and the female helicoidsincluding a helicoid slip region that allows the at least two lensbarrels to rotate and prevents the at least two lens barrels from movingalong the optical axis when one of the at least two lens barrels isretracted into the other. An eccentricity-preventing member provided onthe at least two lens barrels for allowing the at least two lens barrelsto slidably and closely engage with each other so as to slidecircumferentially and slide in the optical axis direction, theeccentricity-preventing member guiding rotation of the at least two lensbarrels via the helicoid slip section when one of the at least two lensbarrels is retreated and slightly advanced with respect to the other ofthe at least two lens barrels.

The eccentricity-preventing member can be formed as a flange whichextends circumferentially and projects radially inward from an innerperiphery of one of the at least two lens barrels which is providedoutside of the other of the at least two lens barrels, the flange beingformed in the vicinity of the helicoid slip section and slidably placedover an outer periphery of an inner lens barrel of the at least two lensbarrels.

Each of the plurality of lens barrels arranged between a camera body anda frontmost lens barrel can be connected via the helicoid structure, thefront most lens barrel and a first adjacent lens barrel being connectedto each other via a cam structure, and wherein the first adjacent lensbarrel and a second adjacent lens barrel connected thereto constitutethe at least two lens barrels.

A barrier mechanism can be mounted on the frontmost lens barrel, thebarrier mechanism being opened and closed by relative movement of thefrontmost lens barrel and the first adjacent lens barrel in the opticalaxis direction as the zoom lens barrel assembly moves from the retractedposition to the minimally extended position for a photographingoperation.

The present disclosure relates to subject matter contained in JapanesePatent Application Nos. 2001-82089, 2001-82090 and 2001-82092 (filed onMar. 22, 2001) which is expressly incorporated herein by reference intheir entireties.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will be discussed below in detail with referenceto the accompanying drawings, in which:

FIG. 1 is an exploded perspective view showing components of anembodiment of a zoom lens barrel assembly of the present invention;

FIG. 2 is a cross-section showing an upper half of the zoom lens barrelassembly in a retracted state;

FIG. 3 is a cross-section showing the upper half of the zoom lens barrelassembly in a photographing position at the wide-angle extremity;

FIG. 4 is a cross-section showing the upper half of the zoom lens barrelassembly in a photographing position at the telephoto extremity;

FIG. 5 is a perspective view showing the zoom lens barrel assembly in afully extended position;

FIG. 6 is a perspective view showing the zoom lens barrel assembly ofFIG. 5 with some of the lens barrels removed;

FIG. 7 is a perspective view of the zoom lens barrel assembly of FIG. 6in a further disassembled state;

FIG. 8 is a perspective view showing elements of a first outer barreland a second outer barrel;

FIG. 9 is a perspective view showing an element of a third linear guidering;

FIG. 10 is an exploded perspective view showing the third linear guidering along with a shutter unit;

FIG. 11 is a developed view of the third linear guide ring showing a camgroove for adjusting a diaphragm;

FIG. 12 is an developed view of a cam ring showing profiles of camgrooves on the inner surface of the cam ring;

FIG. 13 is a block diagram showing a control system of the zoom lensbarrel assembly, the overall structure of which is shown in FIGS. 2through 4;

FIG. 14 is an explanatory developed view showing engagement of thesecond outer barrel, the second helicoid ring, the second linear guidering and guide heads, in a retracted position of the zoom lens barrelassembly;

FIG. 15 is an explanatory developed view showing engagement of thesecond outer barrel, the second helicoid ring, the second linear guidering and the guide heads, in a telephoto extremity position of the zoomlens barrel assembly;

FIG. 16 is an explanatory developed view showing engagement of thesecond outer barrel, the second helicoid ring, the second linear guidering and the guide heads, in an assembly/disassembly position of thezoom lens barrel assembly;

FIG. 17 is a developed view showing engagement of the second outerbarrel, the second helicoid ring, the second linear guide ring and theguide heads, in the assembly/disassembly position of the zoom lensbarrel assembly with the second outer barrel removed;

FIG. 18A is a perspective view showing a longitudinal cross-section ofthe second linear guide ring 25 of the zoom lens barrel assembly;

FIG. 18B is a perspective view showing a longitudinal cross-section ofthe third linear guide ring 18 of the zoom lens barrel assembly;

FIG. 19 is a developed view showing the second linear guide ring of thezoom lens barrel assembly;

FIG. 20 is a developed view showing engagement of female helicoids ofthe second linear guide ring with male helicoids of the third outerbarrel in the retracted position of the zoom lens barrel assembly;

FIG. 21 is a developed view showing engagement of the female helicoidsof the second linear guide ring with the male helicoids of the thirdouter barrel, when the zoom lens barrel assembly extends to a slipsection boundary position;

FIG. 22 is a developed view showing engagement of the female helicoidsof the second linear guide ring with the male helicoids of the thirdouter barrel, when the zoom lens barrel assembly extends to awide-extremity position;

FIG. 23 is a developed view of the first linear guide ring of the zoomlens barrel assembly;

FIG. 24 is a developed view showing engagement of the first linear guidering, the second outer barrel and the second helicoid ring, when thezoom lens barrel assembly is in the retracted position;

FIG. 25 is a developed view showing engagement of the first linear guidering, the second outer barrel and the second helicoid ring, when thezoom lens barrel assembly is in the slip section boundary position;

FIG. 26 is a developed view showing engagement of the first linear guidering, the second outer barrel and the second helicoid ring, when thezoom lens barrel assembly is in the wide-angle extremity position;

FIG. 27A is an explanatory view showing engagement of the femalehelicoids and the helicoid slip section of the first linear guide ring,and the male helicoids of the second helicoid ring of the zoom lensbarrel assembly when the lens barrel assembly is in the retracted state;

FIG. 27B is an explanatory view showing engagement of the femalehelicoids and the helicoid slip section of the first linear guide ring,and the male helicoids of the second helicoid ring of the zoom lensbarrel assembly when the lens barrel assembly is in the slip sectionboundary section;

FIG. 27C is an explanatory view showing engagement of the femalehelicoids and the helicoid slip section of the first linear guide ring,and the male helicoids of the second helicoid ring of the zoom lensbarrel assembly when the lens barrel assembly is in the wide-angleextremity position;

FIG. 28A is an explanatory view showing profile of the female helicoidsand the helicoid slip section of the first linear guide ring;

FIG. 28B is an explanatory view illustrating the problem that arisesupon manufacturing of a mold;

FIG. 28C is an explanatory view illustrating a solution to the problemproposed by an embodiment of the present invention;

FIG. 29 is a cross-section of the upper half of the zoom lens barrelassembly in the retracted state, in which a circumferential flange isformed on the inner peripheral of the first linear guide ring and on theinner peripheral of the second linear guide ring, near the respectiverear ends thereof;

FIG. 30 is a cross-section of the upper half of the zoom lens barrelassembly in a photographing position at the wide-angle extremity, inwhich a circumferential flange is formed on the inner peripheral of thefirst linear guide ring and on the inner peripheral of the second linearguide ring, near the respective rear ends thereof;

FIG. 31 is an enlarged partial cross-section of the upper end of thezoom lens barrel assembly showing adjacent area of a shutter unit withlens barriers closed;

FIG. 32 is an enlarged partial cross-section of the upper end of thezoom lens barrel assembly similar to FIG. 24, with the lens barriersopen;

FIG. 33 is a perspective view of the first helicoid ring and the firstouter barrel, showing a telephoto-extremity stopper of the zoom lensbarrel assembly;

FIG. 34 is a developed view showing the first helicoid ring of the zoomlens barrel assembly;

FIG. 35 is a perspective view showing the bottom of the zoom lens barrelassembly in the telephoto extremity position;

FIG. 36 is a perspective view of the first helicoid ring and the firstouter barrel, showing a construction to prevent a flexible printedcircuit board of the zoom lens barrel assembly from interfering with thegear teeth of the first helicoid ring;

FIG. 37 is a perspective view showing the manner in which the flexibleprinted circuit board interferes with the gear teeth of the firsthelicoid ring; and

FIG. 38 is a partial enlarged perspective view showing the manner inwhich the flexible printed circuit board interferes with the gear teethof the first helicoid ring.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The present invention will now be described in detail hereinafter withreference to the accompanying drawings. In one embodiment, the presentinvention is applied to a four-stage-extension zoom lens barrel assembly(multi-stage-extension zoom lens barrel assembly).

As shown in FIGS. 1 through 5, the zoom lens barrel assembly isconstructed as a four-stage-extension zoom lens barrel assembly andincludes a fixed barrel (rearmost barrel) 12 secured to a camera body,and a four-stage barrel unit which is retained in the fixed barrel 12and advances and retreats along the optical axis relative to the fixedbarrel 12. The four-stage lens unit includes a first outer barrel 17which is the rearmost barrel, a second outer barrel 23 which is thesecond rearmost barrel, a third outer barrel 30 which is the thirdrearmost barrel and is constructed as a cam ring, and a fourth outerbarrel (frontmost barrel) 31 which is the fourth rearmost barrel andserves as a lens-retaining barrel.

In the zoom lens barrel assembly, the fixed barrel 12 is connected tothe first outer barrel 17, which in turn is connected to the secondouter barrel 23, which in turn is connected to the third outer barrel30, with each connection provided by a helicoid structure (mechanism).The helicoid mechanisms allow the barrels 17, 23 and 30 to extendoutward from, or into, each other. The fourth outer barrel 31 isconnected to the third outer barrel 30 through a cam structure.

In the zoom lens barrel assembly of the present embodiment, the firstouter barrel 17 and the second outer barrel 23 are made separately fromhelicoid rings. Furthermore, the zoom lens barrel assembly isconstructed so as to be extended past the telephoto extremity position,which is the most extended position of the barrel assembly in normaloperation, to an assembly/disassembly position, at which the first outerbarrel 17 and the second outer barrel 23 can be removed from and mountedonto the zoom lens barrel assembly. In this embodiment, the barrelassembly is brought into the assembly/disassembly position by rotatingit to an additional rotation angle of 8° from the telephoto extremityposition.

Lens barriers 92 and 93 are mounted on the fourth outer barrel 31 in thefront portion thereof. The lens barriers 92 and 93 are opened and closedas the fourth outer barrel 31 and the third outer barrel 30 move alongthe optical axis relative to each other when the barrel assembly movesbetween the retracted position and the minimally extended photographingposition (which corresponds to the wide-angle extremity position in thisembodiment).

In the zoom lens barrel assembly of the present embodiment, the helicoidstructure to move the second outer barrel 23 and the third outer barrel30 includes a slip section which permits rotation of the second and thethird outer barrels 23 and 30 but does not permit relative movementthereof along the optical axis when the lens barrel assembly movesbetween the retracted position and the wide-angle position. In otherwords, the path of the telescopic movement of the lens barrel assemblyfrom the retracted position toward the wide-angle position includes aslip section in which the second outer barrel 23 and the third outerbarrel 30 rotate at the same speed and do not move relative to eachother along the optical axis. In the slip section, the first outerbarrel 17 rotates while moving along the optical axis, whereas thefourth outer barrel 31 does not rotate but moves relative to the thirdouter barrel 30 along the optical axis. This relative movement betweenthe fourth outer barrel 31 and the third outer barrel 30 along theoptical axis causes opening/closing of the barriers 92 and 93.

The entire structure of the zoom lens barrel assembly will now bedescribed with reference to FIGS. 1 through 7. Referring to FIG. 1,major components of the zoom lens barrel assembly are shown in anexploded view. Hereinafter, “front” refers to the direction toward anobject to be photographed and “rear” refers to the direction toward thecamera body (film).

Female helicoids 12 a are formed on the inner periphery of the fixedbarrel 12 which is secured to a camera body 11. The female helicoids 12a engage with male helicoids 14 a formed on the outer periphery of afirst helicoid ring 14. Arranged on the outside of the fixed barrel 12is a pinion 16, which is rotated by a zooming motor 15. The pinion 16engages with gear teeth 14 b, which are formed on the outer periphery ofthe first helicoid ring 14 and extend along the male helicoids 14 awhere some of the male helicoids 14 a have been removed (cut-away). Thefirst outer barrel 17 is connected to the first helicoid ring 14 at thefront end of the helicoid ring 14.

Engagement portions 141 (see FIGS. 1 and 34) formed on the front end ofthe first helicoid ring 14 engage with engagement portions 171 formed onthe rear end of the first outer barrel 17, so that the first helicoidring 14 integrally rotates with the first outer barrel 17. Theengagement portions 141 and 171 can be brought into disengagableengagement by sliding the first helicoid ring 14 and the first outerbarrel 17 along the optical axis toward each other when the firsthelicoid ring 14 and the first outer barrel 17 are in a predeterminedrelative rotational position (assembly/disassembly position).

A first linear guide ring 18, which is supported within the first outerbarrel 17, can be rotated relative to the first outer barrel 17 andmoves along the optical axis together with the first outer barrel 17(i.e., no relative displacement permitted along the optical axis).Linear guide projections 18a formed on the first linear guide ring 18engage with respective linear guide slots 12 b formed on the fixedbarrel 12, so that the first linear guide ring 18, while being supportedwithin the first outer barrel 17, can only move along the optical axis(i.e., can advance and retreat) and cannot rotate relative to the fixedbarrel 12.

A pair of circumferential grooves 172 are formed on the inner peripheryof the first outer barrel 17 and are separated from each other by apredetermined distance along the optical axis. A pair of keys 181,formed on the outer periphery of the first linear guide ring 18, engagewith the respective circumferential grooves 172. Engagement of the keys181 with the respective circumferential grooves 172 permits rotation ofthe first outer barrel 17 relative to the first linear guide ring 18while preventing the relative movement between them along the opticalaxis.

Thus, upon activation of the zooming motor 15, a driving force therefromis transmitted through a series of reduction gears 15 a and the pinion16 to the gear teeth 14 b, to cause the first helicoid ring 14 torotate. The rotation of the first helicoid ring 14 in turn causes theconnected unit of the first helicoid ring 14, the first outer barrel 17and the first linear guide ring 18, to advance and retreat along theoptical axis. Consequently, the first helicoid ring 14, together withthe first outer barrel 17, advances or retreats along the optical axiswhile rotating as the male helicoids 14 a mesh with the female helicoids12 a, whereas the first linear guide ring 18 advances or retreats alongthe optical axis together with the first helicoid ring 14 and the firstouter barrel 17 without rotating.

The engagement portions 141 and the engagement portions 171, and thekeys 181 and the circumferential grooves 172, are respectivelyconfigured so that when the first helicoid ring 14 and the first outerbarrel 17, and the first outer barrel 17 and the first linear guide ring18, are in their respective predetermined relative rotational positions(assembly/disassembly positions), the first helicoid ring 14 and thefirst outer barrel 17, and the first outer barrel 17 and the firstlinear guide ring 18, can be moved along the optical axis toward andaway from each other for engagement/disengagement.

The first helicoid ring 14, together with the first outer barrel 17,advances and retreats along the optical axis while rotating as the malehelicoids 14 a mesh with the female helicoids 12 a, whereas the firstlinear guide ring 18 advances and retreats along the optical axistogether with the first helicoid ring 14 and the first outer barrel 17without rotating. A brush 19 and a code plate 20, which are secured tothe first linear guide ring 18 and to the fixed barrel 12, respectively,detect predetermined stepped zoom positions (1 (Wide-extremity position)through 7 (Tele-extremity position)) of the first linear guide ring 18along the optical axis with respect to the fixed barrel 12, wherein eachof the stepped zoom positions are separated by a predetermined distance.A cosmetic ring 174 is secured to the front end of the first outerbarrel 17. The brush 19 and the code plate 20 constitute a focaldetecting device.

Female helicoids 18 b are formed on the inner periphery of the firstlinear guide ring 18, and engage with male helicoids 21 a formed on theouter periphery of a second helicoid ring 21. The second helicoid ring21 includes on the outer periphery thereof a pair of guide heads 21 b,which are placed through a pair of guide slots 18 c formed in the firstlinear guide ring 18 and received in a pair of head guide grooves 17 aformed on the inner periphery of the first outer barrel 17 (FIGS. 6 and7). The guide slots 18 c are each formed as an elongate through holethat has the same angle of inclination as the female helicoids 18 b. Asshown in FIG. 8, each head guide groove 17 a is a straight groove thatextends parallel to the optical axis O of the zoom lens system. Whilepart of each guide head 21 b that is placed through the guide slot 18 cis formed to have a cylindrical shape with a circular cross-section, anend of the guide head 21 b that is received in the head guide groove 17a is formed as a rectangular key that extends along the head guidegroove 17 a.

The second outer barrel 23 is connected to the second helicoid ring 21at the front end of the helicoid ring 21. As with the first helicoidring 14 and the first outer barrel 17, the second helicoid ring 21 andthe second outer barrel 23 are connected to each other through theengagement between engagement portions (recesses) 211 formed on thefront end of the helicoid ring 21 and engagement portions (projections)231 formed on the rear end of the second outer barrel 23 such that thesecond helicoid ring 21 integrally rotates with the second outer barrel23 and can integrally retreat and advance. As with the engagementportions 141 and 171, the engagement portions 211 and 231 can be broughtinto disengagable engagement when the second helicoid ring 21 and thesecond outer barrel 23 are in a predetermined relative rotationalposition (assembly/disassembly position).

A second linear guide ring 25 is supported within the second outerbarrel 23, and can be rotated relative to the second outer barrel 23 andmoves along the optical axis together with the second outer barrel 23(i.e., no relative displacement thereof is permitted along the opticalaxis). Linear guide projections 25 a formed on the second linear guidering 25 engage with respective linear guide slots 18 d formed on thefirst linear guide ring 18, so that the second linear guide ring 25 canonly move along the optical axis relative to the first linear guide ring18.

A pair of circumferential grooves 232 are formed on the inner peripheryof the second outer barrel 23 and are separated from one another by apredetermined distance along the optical axis. A pair of keys 251,formed on the outer periphery of the second linear guide ring 25, engagewith the respective circumferential grooves 232. Engagement of the keys251 with the respective circumferential grooves 232 permits rotation ofthe second outer barrel 23 relative to the second linear guide ring 25while preventing the relative movement between them along the opticalaxis.

Thus, upon activation of the zooming motor 15, a driving force therefromis transmitted through the series of the reduction gears 15 a and thepinion 16, to cause the first helicoid ring 14 and the first outerbarrel 17 to advance or retreat while rotating and the first guide ring18, to advance or retreat along the optical axis without rotating. Thisin turn causes the connected unit including the second helicoid ring 21,the second outer barrel 23 and the second linear guide ring 25, toadvance and retreat along the optical axis. Consequently, the secondhelicoid ring 21 and the second outer barrel 23 advance or retreat alongthe optical axis relative to the first outer barrel 17 due to theengagement of the guide heads 21 b with the respective guide slots 18 cand the head guide grooves 17 a, while rotating along with the firstouter barrel 17 as the male helicoids 21 a mesh with the femalehelicoids 18 b. On the other hand, the second linear guide ring 25advances or retreats together with the second helicoid ring 21 and thesecond outer barrel 23 without rotating, due to the engagement of thelinear guide projections 25 a with the respective linear guide slots 18d.

The engagement portions 211 and the engagement portions 231, and thekeys 251 and the circumferential grooves 232, are respectivelyconfigured so that when the second helicoid ring 21 and the second outerbarrel 23, and the second outer barrel 23 and the second linear guidering 25, are in their respective predetermined relative rotationalpositions (assembly/disassembly positions), the second helicoid ring 21and the second outer barrel 23, and the second outer barrel 23 and thesecond linear guide ring 25, can be moved along the optical axis towardand away from each other for engagement/disengagement.

As with the first linear guide ring 18, female helicoids 25 b are formedon the inner peripheral of the second linear guide ring 25. The femalehelicoids 25 b engage with male helicoids 30 a formed on the rear outerperiphery of the third outer barrel (cam ring) 30. The third outerbarrel 30 also serves as a third helicoid ring and includes a pair ofguide heads 30 b on the rear outer surface thereof. The pair of theguide heads 30 b are placed through a pair of guide slots 25 c formed inthe second linear guide ring 25 and are received in a pair of head guidegrooves 23 a formed on the inner periphery of the second outer barrel 23(see FIGS. 8 and 14). While part of each guide head 30 b that is placedthrough the guide slot 25 c is formed to have a cylindrical shape with acircular cross-section, an end of the guide head 30 b that is receivedin the head guide groove 23 a is formed as a rectangular shape thatextends along the head guide groove 23 a.

The guide slots 25 c are each formed as an elongate through hole thathas the same angle of inclination as the female helicoids 25 b. Eachhead guide groove 23 a is a straight groove that extends parallel to theoptical axis O.

A third linear guide ring 33 is supported within the third outer barrel30, which can be rotated relative to the third outer barrel 30 and movesintegrally with the third outer barrel 30 along the optical axis (i.e.,no relative displacement thereof is permitted along the optical axis).The third linear guide ring 33 includes on the outer periphery thereof aplurality of linear guide projections 33 a, each of which engages with alinear guide slot 25 d formed on the inner periphery of the secondlinear guide ring 25, allowing the third linear guide ring 33 to moveonly along the optical axis.

Thus, upon activation of the zooming motor 15, the first helicoid ring14 and the first outer barrel 17 advance or retreat along the opticalaxis while rotating. The first linear guide ring 18 advances or retreatsalong the optical axis together with the first helicoid ring 14 and thefirst outer barrel 17 without rotating. The second helicoid ring 21 andthe second outer barrel 23 advance or retreat relative to each otheralong the optical axis while rotating together at the same rotationspeed with respect to the first outer barrel 17. The second linear guidering 25 advances or retreats together with the second helicoid ring 21and the second outer barrel 23 without rotating. As a result, as themale helicoids 30 a mesh with the female helicoids 25 b, the third outerbarrel 30 and the third linear guide ring 33 advance or retreat alongthe optical axis with respect to the second outer barrel 23, whilerotating together with the second outer barrel 23 at the same rotationspeed due to the engagement of the guide heads 30 b with the guide slots25 c and the head guide grooves 23 a. The third linear guide ring 33,with the restriction of the linear guide projections 33 a engaging thelinear guide slots 25 d, advances or retreats along the optical axistogether with the third outer barrel 30 without rotating. A portion ofthe third outer barrel 30 in front of the helicoids 30 a extends fromthe second outer barrel 23 and is exposed outside to form a part of theexternal appearance of the lens barrel.

The fourth outer barrel (lens-retaining barrel) 31, which holds a firstlens group L1 (which includes a first sub-lens group S1 and a secondsub-lens group S2), and a rear lens group frame 32 including a securedsecond lens group L2, are supported within the third outer barrel 30,with the fourth outer barrel 31 being in front of the rear lens groupframe 32. The fourth outer barrel 31 and the rear lens group frame 32are guided along the optical axis by the third linear guide ring 33.Specifically, the third linear guide ring 33 includes three arm members33 b, each having a partial cylindrical shape as shown in FIGS. 9 and10. Each arm member 33 b includes on respective sides thereof (i.e., theouter periphery and the inner periphery) linear guide slots 33 c and 33d, each of which extends parallel to the optical axis O. Each guide slot33 c slidably receives a linear guide projection (not shown) provided onthe inner periphery of the fourth outer barrel 31, whereas each guideslot 33 d slidably receives a linear guide projection 32 a provided onthe outer periphery of the rear lens group frame 32.

Front lens group cam grooves 35 for the fourth outer barrel 31 and rearlens group cam grooves 36 for the rear lens group frame 32 are formed onthe inner periphery of the third outer barrel 30. The front lens groupcam grooves 35 and the rear lens group cam grooves 36 are shown in adeveloped view in FIG. 12. As shown in FIG. 12, three front lens groupcam grooves 35 and three rear lens group cam grooves 36 are alternatelyarranged in the circumferential direction and are equally spaced fromone another. Front lens group follower projections 31 a and rear lensgroup follower projections 32 b radially protrude from the fourth outerbarrel 31 and the rear lens group frame 32, respectively, for engagingthe front lens group cam grooves 35 and the rear lens group cam grooves36, respectively.

Accordingly, when the zooming motor 15 is activated and the third outerbarrel 30 advances or retreats along the optical axis while rotatingtogether with the first outer barrel 17 and the second outer barrel 23,and the third linear guide ring 33 advances or retreats along theoptical axis together with the third outer barrel 30 without rotating,the fourth outer barrel 31 and the rear lens group frame 32, while beingprevented from rotating by the engagement of the linear guideprojections (not shown) with the linear guide slots 33 c, advance orretreat along the optical axis on a predetermined path with respect tothe third outer barrel 30 due to the engagement of the followerprojections 31 a and 32 b with the respective cam grooves 35 and 36.

The follower projections 31 a and 32 b and the respective cam grooves 35and 36, which cause the fourth outer barrel 31 and the rear lens groupframe 32 to move toward and away from each other along the optical axis,constitute a zoom cam mechanism.

A portion of the fourth outer barrel 31 in front the followerprojections 31 a extends from the third outer barrel 30 and is exposedoutside to form a part of the external appearance of the lens barrel.

The above-described zoom lens barrel has a construction in which thefirst linear guide ring 18, the second linear guide ring 25, the thirdlinear guide ring 33, and the fourth outer barrel 31 advance and retreatlinearly along the optical axis with respect to the fixed barrel 12,without rotating.

As shown in FIG. 12, the region of each front lens group cam groove 35and the region of each rear lens group cam groove 36 extending betweenrespective telephoto extremity positions (indicated as T-extremity) andretracted positions (indicated as retracted) are used in normaloperations. During photographing, the follower projection 31 a and thefollower projections 32 b are each guided over the normal operationregion between the telephoto extremity position (T-extremity) and thewide-angle extremity position (W-extremity). The rear lens group camgroove 36 has an intermediate discontinuous position 36 a between thetelephoto extremity position (T-extremity) and the wide-angle extremityposition. Between the telephoto extremity position and the wide-angleextremity position, the first lens group L1, retained within the fourthouter barrel 31, which is guided over the front lens group groove 35,has a switching function in which the first sub-lens group S1 and thesecond sub-lens group S2 is switched between a mutually close position(tele mode) and a mutually distant position (wide mode). Upon switchingin the first lens group L1, the second lens group L2 passes theintermediate discontinuous position 36 a in the rear lens group camgroove 36. The zoom lens system is controlled such that the intermediatediscontinuous position 36 a is not used as an actual zooming rangeduring a photographing operation (i.e., the third outer barrel 30 doesnot come to a stop thereat).

The lens group cam grooves 35 and 36 include an assembly/disassemblyposition beyond the telephoto extremity position, to which the zoom lensbarrel needs to be rotated for assembly/disassembly.

A shutter unit 40 is arranged within the fourth outer barrel 31. A frontsub-lens group frame 45 and a rear sub-lens group frame 46 are fitted inthe shutter unit 40. The first sub-lens group S1 is secured to the frontsub-lens group frame 45, and the second sub-lens group S2 is secured tothe rear sub-lens group frame 46. The relative position of the frontsub-lens group frame 45 (first sub-lens group S1) with respect to therear sub-lens group frame 46 (second sub-lens group S2) along theoptical axis is switched between two positions, namely, the mutuallydistant position for wide-angle photographing and a mutually closeposition for telephoto photographing. The switching is performed betweenthe wide-angle extremity and the telephoto extremity via a focusing cammechanism, which is driven by a bi-directional motor 53. In eachposition, the sub-lens groups S1 and S2 are advanced or retreated alongthe optical axis for focusing by the bi-directional motor 53 through thefocusing cam mechanism.

The shutter unit 40 is also provided behind the second sub-lens group S2with a lens shutter device which includes shutter sectors 60, and adiaphragm mechanism which includes diaphragm sectors 62 (see FIGS. 2 and3). In the zoom lens barrel of the present embodiment, the shuttersectors 60 are blades that serve both as a variable aperture todetermine an f-number, and as a shutter. The shutter sectors 60 areelectrically controlled by a control circuit 81 so that when the shutteris released, the degree of opening of the shutter sectors 60 (f-number)and time that the shutter sectors 60 remain open (shutter speed) varydepending on the exposure value. On the other hand, the diaphragmsectors 62 are provided for the purpose of limiting the maximum aperturesize especially during wide-angle photographing. The degree of openingof the diaphragm sectors 62 is mechanically varied depending on how farthe entire zoom lens barrel needs to extend outward. In other words, thediaphragm sectors 62 limit the aperture size so that unwanted light isnot collected during wide-angle photographing.

A diaphragm drive ring 63 for opening and closing the diaphragm sectors62 includes on the periphery thereof a lug 63 b, which engages with adiaphragm-controlling cam slot 71 formed on the inner periphery of thepartial cylindrical arm member 33 b of the third linear guide ring 33(see FIG. 10). Upon zooming, the third linear guide ring 33 and theshutter unit 40 (diaphragm drive ring 63) move relative to each otheralong the optical axis. This causes the lug 63 b to follow thediaphragm-controlling cam slot 71 and move in the circumferentialdirection. This in turn causes the diaphragm drive ring 63 to rotateand, as a result, the size of the aperture formed by the diaphragmsectors 62 is varied.

As shown in FIG. 11, the diaphragm-controlling cam slot 71 includes astraight portion 71 a extending parallel to the optical axis O, a slopedportion 71 b sloped with respect to the optical axis O, and an openingportion 71 c opening to the front of the third linear guide ring 33. Thestraight portion 71 a and the sloped portion 71 b each havesubstantially the same width as the lug 63 b so that the lug 63 bengages therewith with substantially no play.

Electric components of the shutter unit 40 are connected to the controlcircuit 81 (see FIG. 13) in the camera body via a flexible printedcircuit board (FPC) 80. The positions of folds in the FPC 80 movedepending on the change in the relative position of the shutter unit 40with respect to the control circuit 81 as the zoom lens barrel advancesand retreats. The FPC 80 is folded into a z-shape to avoid interferencewith the other components of the barrel and is inserted between theouter barrels.

In the present embodiment, the FPC 80 is folded on top of itself andforms overlapped portions 801 and 802 (see FIGS. 2 and 3). Theoverlapped portions 801 and 802 are inserted from the rear side of thezoom lens barrel assembly into a gap formed between the first outerbarrel 17 and the first linear guide ring 18 and a gap formed betweenthe second outer barrel 23 and the second linear guide ring 25,respectively. The portion of the FPC 80 that comes out from between thesecond outer barrel 23 and the second linear guide ring 25 extendsacross the third outer barrel 30 into the fourth outer barrel 31 and isconnected to the shutter unit 40 at one end thereof.

The other end of the FPC 80 is pulled out from the front end of thefixed barrel 12 (FIGS. 2, 3 and 4). The miniaturized construction of thecamera poses a limitation to the choice of the position at which the FPC80 is pulled out. For this reason, the FPC 80 is positioned in theproximity of the helicoids 14 a and the gear teeth 14 b of the firsthelicoid ring 14 across the path of the helicoids 14 a and the gearteeth 14 b. This can result in the FPC 80 intersecting the path of endsof the gear teeth 14 b (see FIGS. 36, 37 and 38). If the FPC 80 bends insuch a construction, the FPC 80 may catch on an end tooth 14 b 1 of thegear teeth 14 b as shown in FIGS. 37 and 38. However, the presentembodiment employs a lead 14 a 1 formed on the first helicoid ring 14along the path of the gear teeth 14 b for avoiding such interference(see FIG. 34).

Furthermore, the front end tooth 14 b 1 of the gear teeth 14 b serves asa stopper that comes into contact with a telephoto extremity stopper 101to prevent further rotation of the first helicoid ring 14 (see FIG. 33).In the present embodiment, a stopper space 14 c is provided where thegear teeth 14 b terminate in order to permit engagement of the telephotoextremity stopper 101 (see FIG. 34).

As shown in FIG. 13, the zooming motor 15 for the first helicoid ring14, the bi-directional motor 53 for the front sub-lens group frame 45and rear sub-lens group frame 46, and the shutter unit 40 are controlledby a control circuit (control device) 81. Focal length information 81 a,which is set by the user (photographer) via a zoom switch or the like,detected object distance information 81 b, which is provided by a objectdistance measuring device, and object brightness information 81 c, whichis provided by a object brightness measuring device are input to thecontrol circuit 81.

The above-described zoom lens barrel assembly of the present inventionoperates in the following manner. Upon the zooming motor 15 driving thepinion 16, the first helicoid ring 14 and the first outer barrel 17advance or retreat while rotating. The first linear guide ring 18advances or retreats together with the first helicoid ring 14 and thefirst outer barrel 17 along the optical axis without rotating.

The second helicoid ring 21 and the second outer barrel 23, whilerotating together at the same rotation speed with respect to the firstouter barrel 17, advance or retreat relative to one another along theoptical axis. The second linear guide ring 25 advances or retreats alongthe optical axis together with the second helicoid ring 21 and thesecond outer barrel 23 without rotating.

The third outer barrel 30 advances or retreats along the optical axiswith respect to the second outer barrel 23, while rotating at the samerotation speed. The third linear guide ring 33 advances or retreatsalong the optical axis together with the third outer barrel 30 withoutrotating.

The fourth outer barrel 31 advances or retreats along the optical axiswithout rotating (The third outer barrel 30 rotates with respect to thefourth outer barrel 31).

As a result, the fourth outer barrel 31 (first lens group L1) and therear lens group frame 32 (second lens group L2), each guided along theoptical axis in the third outer barrel 30, move relative to each otheralong the optical axis on a predetermined path provided by the frontlens group cam grooves 35 and the rear lens group cam grooves 36.

For example, in the retracted state of the zoom lens barrel assembly asshown in FIG. 2, the zoom lens barrels are substantially retracted intothe camera body 11. When the zooming motor 15 is driven in the directionto extend the barrels, the zoom lens barrel assembly extends outward toassume the photographing position at the wide-angle extremity as shownin FIG. 3. By further driving the zooming motor 15 in the direction toextend the barrels, the zoom lens barrel assembly extends outward fromthe wide-angle photographing position to the photographing position atthe telephoto extremity as shown in FIG. 4.

In the present embodiment, the telephoto extremity stopper 101 serves tostop rotation of the first helicoid ring 14 in order to prevent the zoomlens barrel assembly from further extending out from the telephotophotographing position during normal operation. As shown in FIG. 33, thetelephoto extremity stopper 101 engages with the end tooth 14 b 1 of thefirst helicoid ring 14, thereby preventing further rotation of the firsthelicoid ring 14.

The first helicoid ring 14 is shown in a developed view in FIG. 34. Thebottom side of FIG. 34 corresponds to the front side of the zoom lensbarrel assembly. The first helicoid ring 14 rotates while being led bythe male helicoids 14 a to advance or retreat. The telephoto extremitystopper 101 is positioned in the path of the gear teeth 14 b since thegear teeth 14 b are formed along the male helicoids 14 a. The telephotoextremity stopper 101 is attached to the fixed barrel 12 and isexternally secured to the fixed barrel 12 by a screw (see FIG. 35). Byemploying such a telephoto extremity stopper 101, which can beexternally removed from the fixed barrel 12, the assembly/disassembly ofthe zoom lens barrel assembly can be facilitated.

Note that the outer diameter of the outermost ends of the gear teeth 14b is larger than the outer diameter of the first outer barrel 17.

By further driving the zooming motor 15 in the direction to extend thebarrels with the telephoto extremity stopper 101 removed, the firsthelicoid ring 14, the first outer barrel 17 and the second outer barrel23 are made to further rotate. This causes the zoom lens barrel assemblyto extend out from the telephoto photographing position to theassembly/disassembly position of the first outer barrel 17 and thesecond outer barrel 23 as shown in FIG. 5. In this embodiment, the zoomlens barrel assembly is brought into the assembly/disassembly positionby rotating the first helicoid ring 14 by additional 8° from thetelephoto photographing position. FIG. 6 shows the zoom lens barrelassembly in the assembly/disassembly position with the first and thesecond outer barrels 17 and 23 removed.

By driving the zooming motor 15 in the reverse direction to retreat thebarrels, the zoom lens barrel assembly is made to retreat from theassembly/disassembly position, to the telephoto photographing position,then to the wide-angle photographing position, and then to the retractedposition. In practice, zooming is controlled in a stepwise manner:several focal length steps are provided between the wide-angle extremityand the telephoto extremity, and the zooming motor 15 is stopped at eachfocal length step to perform focusing and exposure. As described above,the region assigned to the switching of the movement of the firstsub-lens group S1 and the second sub-lens group S2 toward and away fromeach other is not used for photographing. For this reason, no step isprovided in this region so that the third outer barrel 30 (thus, thezooming motor 15) does not come to a stop in this region.

In FIG. 14, the second outer barrel 23, the second helicoid ring 21, thesecond linear guide ring 25 and the guide heads 30 b in the retractedposition are shown in a developed view as viewed from outside. In theretracted position, keys 251, which extend in the circumferentialdirection on the outer periphery of the second linear guide ring 25,engage with respective inner peripheral grooves 232, which extendcircumferentially on the inner periphery of the second outer barrel 23,so that the second outer barrel 23 and the second helicoid ring 21 canrotate relative to one another and move together along the optical axis.A total of four keys 251 are provided on the outer circumference of thelinear guide ring 25. Two keys 251 are provided at the samecircumferential position spaced apart by a predetermined length alongthe optical axis, and the other two keys 251 are provided at adiametrically opposite circumferential position to the other keys 251and are spaced apart by the same predetermined length along the opticalaxis as that of the other two keys 251. The guide heads 30 b are eachplaced in a slip region 25 c 1 of the guide slot 25 c.

The slip region 25 c 1 of the guide slot 25 c serves as a slip sectionfor allowing the third outer barrel 30 to rotatably slip. In otherwords, when the guide head 30 b is in the slip region 25 c 1 and movesalong the slip region 25 c 1, rotation of the third outer barrel 30 withrespect to the second linear guide ring 25 does not cause relativemovement between the third outer barrel 30 and the second linear guidering 25 along the optical axis. The slip region 25 c 1 is provided inthe section between the retracted position and the wide angle extremityposition of the zoom lens barrel assembly.

By further driving the zooming motor 15 in the direction to extend thebarrels, the zoom lens barrel assembly is brought into the telephotoextremity position. The second outer barrel 23, the second helicoid ring21, the second linear guide ring 25 and the guide heads 30 b in thetelephoto extremity position are shown in FIG. 15 in a developed viewsimilar to FIG. 14. In the telephoto extremity position, while a portionof each key 251 has come out from the circumferential groove 232 into afree space 233, a portion of each key 251 still remains in thecircumferential groove 232. Accordingly, the second outer barrel 23 isprevented from moving with respect to the second linear guide ring 25along the optical axis (thus, the second outer barrel 23 does not comeoff the second linear guide ring 25). In other words, the second outerbarrel 23 and the second linear guide ring 25 can rotate relative toeach other but advance or retreat together along the optical axis.

At this stage, when the zooming motor 15 is driven in the direction toextend the barrels, the gear teeth 14 b of the first helicoid ring 14engage with the telephoto extremity stopper 101 and prevent the firsthelicoid ring 14 from rotating further.

By removing the telephoto extremity stopper 101, the first helicoid ring14 is made to move freely so that the zooming motor 15 can be furtherdriven to extend the barrels.

From the above-described telephoto extremity position, the zoom lensbarrel assembly is brought into the assembly/disassembly position byremoving the telephoto extremity stopper (not shown) and further drivingthe zooming motor 15 in the direction to extend the barrels. The secondouter barrel 23, the second helicoid ring 21, the second linear guidering 25 and the guide heads 30 b in the assembly/disassembly positionare shown in FIG. 16 in a developed view similar to FIG. 14. In theassembly/disassembly position, each key 251 has come out of thecircumferential groove 232 and is entirely in the free space 233. Thus,in the assembly/disassembly position, the second outer barrel 23 can bemoved with respect to the second linear guide ring 25 along the opticalaxis. In other words, the second outer barrel 23 can be removed from(see FIG. 17) or mounted back onto the second linear guide ring 25 (FIG.16).

By pulling out the first and the second outer barrels 17 and 23 in theassembly/disassembly position, the guide heads 21 b and 30 b can beexternally exposed (see FIG. 6). Once the guide heads 21 b and 30 b havebeen removed (see FIG. 7), the third outer barrel 30, the secondhelicoid ring 21, and the first helicoid ring 14 can be further rotatedto extend further outward for removal by the action of the helicoids.Thus, the zoom lens barrel assembly can be disassembled when in theassembly/disassembly position.

The zoom lens barrel assembly of the present invention is integratedwith the camera body and is constructed such that when the zoom lensbarrel is assembled to allow the camera to take pictures, rotation ofthe zooming motor 15 is controlled to prevent the lens barrel assemblyfrom extending out past the telephoto photographing position to theassembly/disassembly position. If the camera needs repairing, thezooming motor 15 can be made to operate to bring the zoom lens barrelassembly from the telephoto photographing position into theassembly/disassembly position by, for example, entering specialcommands.

In this embodiment, as with the second outer barrel 23 and the secondlinear guide ring 25, the first outer barrel 17 and the first linearguide ring 18 have circumferential grooves 172, free spaces 173, andkeys 181. The first outer barrel 17 can be removed from, and mountedonto, the first linear guide ring 18 in the above-describedassembly/disassembly position.

A lens barrier mechanism for opening and closing the barrel opening infront of the first lens group L1 is arranged in the front portion of thefourth outer barrel 31. The lens barrier mechanism includes a cosmeticplate 90 secured to the front portion of the fourth outer barrel 31, abarrier drive ring 91, which is retained in a front wall 31 b (see FIG.2) of the fourth outer barrel 31 and can rotate about the optical axisO, a pair of outer barriers 92 and a pair of inner barriers 93, whichare each rotatably supported between the barrier drive ring 91 and thecosmetic plate 90. The cosmetic plate 90 includes a projection (notshown) for rotatably supporting the outer barriers 92 and the innerbarriers 93. The outer barriers 92 and the inner barriers 93 pivot aboutthe projection and cooperate to open and close the opening of thecosmetic plate 90. A barrier biasing spring 94 biases each pair of thebarriers 92 and 93 to close.

The barrier drive ring 91 includes a pair of barrier projections 91 aarranged at diametrically opposite ends, and a lug arm 91 b extendingrearward in the optical axis direction. The barrier projections 91 aengage with the outer barriers 92 or the inner barriers 93 to transmitrotation of the barrier drive ring 91 to the barriers 92 and 93. The lugarm 91 b is inserted through a hole (not shown) formed in the front wall31 b arranged on the inner periphery of the front portion of the fourthouter barrel 31 into the fourth outer barrel 31. The lug arm 91 b isshaped to slide against a guide slope 33 e formed on the front end ofthe partial cylindrical arm member 33 b of the third linear guide ring33.

A drive ring biasing spring 95 biases the barrier drive ring 91 torotate to open the barriers 92 and 93. The drive ring biasing spring 95exerts a larger force than the barrier biasing spring 94. Thus, when thebarrier drive ring 91 is free to rotate by the biasing force of thedrive ring biasing spring 95, the biasing force of the drive ringbiasing spring 95 is transmitted through the barrier drive ring 91, attransmitted to the barriers 92 and 93 via the barrier projection 91 a,so that the barriers 92 and 93 are held open against the biasing forceof the barrier biasing spring 94. When the zoom lens barrel assembly isin a photographing position between the wide-angle extremity as shown inFIG. 3 and the telephoto extremity as shown in FIG. 4, the lug arm 91 bis not in contact with the guide slope 33 e and the barrier drive ring91 remains free, so that the barriers 92 and 93 are held open.

As the zoom lens barrel assembly shifts from the wide-angle extremityposition as shown in FIGS. 3 and 32 to the retracted position as shownin FIGS. 2 and 31, the guide slope (barrier drive surface) 33 e (seeFIG. 9) of the third linear guide ring 33 comes into contact with thelug arm 91 b of the barrier drive ring 91 and starts sliding against thelug arm 91 b. As a result, the barrier drive ring 91 is forcibly rotatedagainst the drive ring biasing spring 95 as it follows the guide slope33 e. This allows the barriers 92 and 93 to rotate and close. Since thebarriers 92 and 93 are released from the restriction of the barrierdrive ring 91 and are biased by the biasing force of the barrier biasingspring 94, each pair of the barriers 92 and 93 rotate to close andremain closed.

When the zoom lens barrel assembly shifts from the wide-angle extremityposition to the retracted position, slip sections are utilized so thatthe third outer barrel 30 and the second outer barrel 23, and the secondouter barrel 23 and the first outer barrel 17, rotate together and donot move relative to one another along the optical axis. In the presentembodiment, before the entire zoom lens barrel assembly retreats to theretracted position, i.e., before the fourth outer barrel 31 retreats tothe retracted position thereof with respect to the third outer barrel30, the second outer barrel 23 retreats along the optical axis to theretracted position thereof with respect to the first outer barrel 17,and enters the slip section thereof (i.e., the slip region 25 c 1 of thesecond linear guide ring 25), and thereafter starts retreating whilerotating together with the first outer barrel 17; subsequently, thethird outer barrel 30 retreats along the optical axis to the retractedposition thereof with respect to the second outer barrel 23 and entersthe slip section thereof; and the third outer barrel 30, the secondouter barrel 23, and the first outer barrel 17 start retreating towardthe retracted position while rotating together. Accordingly, either atsubstantially the same time or after the guide slope 33 e of the thirdlinear guide ring 33 comes into contact with the lug arm 91 b of thebarrier drive ring 91 and starts sliding against the lug arm 91 b, thesecond outer barrel 23 and then the third outer barrel 30 reach theirrespective slip sections. As a result, the fourth outer barrel 31retreats due to the relative rotation of the fourth outer barrel 31 withrespect to the third linear guide ring 33. Thus, the fourth outer barrel31 and the third outer barrel 30, and thus the third linear guide ring33, move along the optical axis relative to each other. This causes thebarrier drive ring 91 to rotate to thereby close the barriers 92 and 93.

Conversely, when the zoom lens barrel assembly extends out from theretracted position to the wide-angle extremity position, the first, thesecond, and the third outer barrels 17, 23 and 30, respectively extendout along the optical axis while rotating together. However, the secondouter barrel 23 and the third outer barrel 30, when in each slip sectionthereof, extend out together with the first outer barrel 17 toward thewide-angle extremity while rotating together with the first outer barrel17, whereas the fourth outer barrel 31 extends out toward the wide-angleextremity with respect to the third outer barrel 30 without relativelyrotating. When the second outer barrel 23 and the third outer barrel 30are in the slip sections thereof, the guide slope 33 e of the thirdlinear guide ring 33 moves away from the lug arm 91 b so that thebarrier drive ring 91, actuated by the biasing force of the drive ringbiasing spring 95, rotates to open the barriers 92 and 93. As a result,the guide slope 33 e moves away from the lug arm 91 b and the barriers92 and 93 are completely opened before the zoom lens barrel assemblyreaches the wide-angle extremity.

When the zoom lens barrel assembly extends out from the retractedposition to the wide-angle extremity position, the third outer barrel 30exits the slip section first. Thereafter, the third outer barrel 30starts to extend with respect to the second outer barrel 23.Subsequently, the second outer barrel 23 exits the slip section thereof(i.e., the slip region 25 c 1 of the second linear guide ring 25),causing the second outer barrel 23 to start extending out with respectto the first outer barrel 17.

As described above, the opening/closing of the barriers 92 and 93 iseffected by the stroke, i.e., the relative displacement between thefourth outer barrel 31 and the third outer barrel 30 along the opticalaxis that occurs as the zoom lens barrel assembly shifts from theretracted position to the wide-angle extremity position. Accordingly, analternative construction is possible wherein the slip section is notprovided in the third outer barrel 30 and/or the second outer barrel 23.A large stroke is desirable for opening and closing the barriers 92 and93 since too small a stroke can result in an excessively large drivingtorque. However, increasing the stroke length increases the rotationangle of the third outer barrel 30 required for opening/closing of thebarriers, and as a result, the fourth outer barrel 31 extends by anexcessively large amount with respect to the camera body, which canexceed the required amount for shifting the lens barrel assembly fromthe retracted position to the wide-angle extremity position.

Though the slip section may be provided only in the helicoid structureof the third outer barrel 30, such a construction can result in a smallstroke for the rotation angle of the lens barrel required for theextension of the lens barrel assembly from the retracted position to thewide-angle extremity position. Therefore, in such a case, the slipsection needs to have a large rotation angle. Furthermore, in such aconstruction, relative displacement of the fourth outer barrel 31 withrespect to the third outer barrel 30 along the optical axis becomeslarge, so that the part of the FPC 80 that extends across the thirdouter barrel 30 may be unfavorably tensed unless sufficient play isprovided (refer to FIGS. 2 and 3).

To cope with such problems, the helicoid slip sections are provided bothin the second outer barrel 23 and in the third outer barrel 30 in thepresent embodiment in order to ensure a large rotation angle of the lensbarrel assembly as the lens barrel assemble shifts from the retractedposition to the wide-angle extremity position. In this manner,sufficient relative displacement along the optical axis of the fourthouter barrel 31 with respect to the third outer barrel 30 is achievedfor the small lead of the cam for sending out the fourth outer barrel31.

Construction of the slip section of the helicoids will now be describedwith reference to FIGS. 18 through 27. FIG. 18A is a perspective viewshowing a longitudinal cross-section of the second linear guide ring 25.FIG. 18B is a perspective view showing a longitudinal cross-section ofthe first linear guide ring 18. FIG. 19 is a developed view of thesecond linear guide ring 25. Each of FIGS. 20 through 22 is a developedview showing a relationship between the second linear guide ring 25 andthe third outer barrel (cam/helicoid ring) 30. FIG. 23 is a developedview of the first linear guide ring 18. Each of FIGS. 24 through 26 is adeveloped view showing a relationship between the first linear guidering 18, the second outer barrel 23, and the second helicoid ring 21.Each of FIGS. 27A, 27B and 27C is an enlarged view showing the femalehelicoids 25 b and helicoid slip sections 25 b 1 of the second linearguide ring 25, and the male helicoids 30 a of the third outer barrel 30.

As shown in FIG. 19, the female helicoid 25 b on the inner periphery ofthe second linear guide ring 25 includes a wide (in the circumferentialdirection) helicoid slip section 25 b 1 near the rear end (camera bodyside) of the second linear guide ring 25. The helicoid slip section 25 b1 has substantially the same length as the male helicoid 30 a of thethird outer barrel 30 in the optical axis direction. Accordingly, asshown in FIG. 20, as the male helicoid 30 a proceeds into the helicoidslip section 25 b 1, the male helicoids 30 a and the female helicoids 25b are released from the confinement of the flanks thereof, so that thesecond linear guide ring 25 and the third outer barrel 30 can rotaterelative to each other with the relative movement along the optical axisbeing prevented. The guide slot 25 c also includes the slip section 25 c1 to permit the rotation in the helicoid slip section 25 b 1.

Although the helicoid slip section 25 b 1 is designed to permit nomovement of the male helicoid 30 a along the optical axis, helicoid slipsection 25 b 1 can be designed to permit a slight movement of the malehelicoid 30 a along the optical axis. Furthermore, the helicoid slipsection 25 b 1 can include a thrust surface 25 b 2 (see FIG. 28A) andthe front and the rear end surfaces of the male helicoid 30 a may beconfigured as a flank surface to slide against the thrust surface 25 b2.

When the zoom lens barrel assembly is in the retracted position, themale helicoids 30 a for engaging the female helicoids 25 b are locatedin the respective helicoid slip sections 25 b 1, and the guide heads 30b placed through the guide slots 25 c are located in the respective slipsections 25 c 1 (see FIG. 20). As the zoom lens barrel assembly extendsout from the retracted position toward the wide-angle extremity, thethird outer barrel 30, the male helicoids 30 a, and the guide heads 30 bmove with respect to the second linear guide ring 25 toward thewide-angle position (toward the right-hand side in FIGS. 20 through 22).With the male helicoids 30 a confined in the respective helicoid slipsections 25 b 1, the third outer barrel 30 can only rotate with respectto the second linear guide ring 25, and the zoom lens barrel assemblyproceeds to a position in which the male helicoids 30 a are positionedat the boundaries of the slip sections (slip section boundary position)(see FIG. 21). When the zoom lens barrel assembly is in the slip sectionboundary position, the male helicoids 30 a engage with the femalehelicoid 25 b by their flanks.

As the zoom lens barrel assembly further extends out from the slipsection boundary position toward the wide-angle extremity position, thethird outer barrel 30, with the male helicoids 30 a confined by thefemale helicoids 25 b, moves forward with respect to the second linearguide ring 25 (toward the top of FIGS. 20 through 22) while rotating andbeing led by the female helicoids 25 b. As a result, the zoom lensbarrel assembly proceeds to the wide-angle extremity position (FIG. 22).

Although the male helicoids 30 a are formed on the third outer barrel 30and female helicoids 25 b are formed on the second linear guide ring 25in the present embodiment, male helicoids can be formed on the secondlinear guide ring 25 and female helicoids can be formed on the thirdouter barrel 30.

As with the second linear guide ring 25 and the third outer barrel 30,the first linear guide ring 18, the second outer barrel 23 and thesecond helicoid ring 21 include slip sections.

As shown in FIG. 23, the female helicoid 18 b on the inner periphery ofthe first linear guide ring 18 has a wide (as viewed in thecircumferential direction) helicoid slip section 18 b 1 near the rearend (camera body side) of the first linear guide ring 18. The helicoidslip section 18 b 1 has substantially the same length as the malehelicoid 21 a of the second helicoid ring 21 in the optical axisdirection. Accordingly, as shown in FIG. 24, as the male helicoid 21 aproceeds to the helicoid slip section 18 b 1, the male helicoids 21 aand the female helicoids 18 b are released from the confinement of theflanks thereof, so that the first linear guide ring 18 and the helicoidring 21 (and thus the second outer barrel 23) can rotate relative toeach other with the relative movement along the optical axis beingprevented. The guide slot 18 c also includes a slip section 18 c 1 whichcorresponds to the helicoid slip section 18 b 1 and has no lead angle.

When the zoom lens barrel assembly is in the retracted position, themale helicoids 21 a for engaging with the female helicoids 18 b arelocated in the respective helicoid slip sections 18 b 1, and the guideheads 21 b placed through the guide slots 18 c are located in therespective slip sections 18 c 1 (see FIG. 24 and FIG. 27A). As the zoomlens barrel assembly extends out from the retracted position toward thewide-angle extremity, the male helicoids 21 a and the guide heads 21 b,and thus the helicoid ring 21 and the second outer barrel 23, move withrespect to the first linear guide ring 18 toward the wide-angle position(toward the right-hand side in FIGS. 24 through 26). During thisrelative movement, with the male helicoids 21 a and the guide heads 21 blocated in the helicoid slip sections 18 b 1 and in the slip sections 18c 1, respectively, the second outer barrel 23 and the second helicoidring 21 can only rotate with respect to the first linear guide ring 18,and the zoom lens barrel assembly proceeds to a position in which themale helicoids 21 a are positioned at the boundaries of the slipsections (slip section boundary position) (see FIG. 25 and FIG. 27B).When the zoom lens barrel assembly is in the slip section boundaryposition, the male helicoids 21 a engage with the female helicoids 18 bby their flanks.

As the zoom lens barrel assembly further extends out from the slipsection boundary position toward the wide-angle extremity position, thesecond outer barrel 23 and the second helicoid ring 21, with the malehelicoids 21 a confined by the female helicoids 18 b, move forward withrespect to the first linear guide ring 18 (toward the top of FIGS. 24through 26) and rotate while being led by the male helicoids 21 a, thefemale helicoids 18 b, and the guide slots 18 c. As a result, the zoomlens barrel assembly proceeds to the wide-angle extremity position(shown in FIG. 26 and FIG. 27C).

In this embodiment, the third outer barrel 30 also has slip sectionssince the slipping of only the second outer barrel 23 is insufficientfor the opening/closing of the barriers 92 and 93. For the third outerbarrel 30, the slip sections are provided for the minimizing the amountof barrel advancement and adjusting the balance of barrel advancement.

Furthermore, in the present embodiment, the slip angle of the helicoidslip section 18 b 1 for slipping the second outer barrel 23 and thehelicoid ring 21 is set to be larger than the slip angle of the helicoidslip section 25 b 1 for slipping the third outer barrel 30. If the thirdouter barrel 30 and the second outer barrel 23 simultaneously shift fromthe slip section to the helicoid section, the applied load increasessignificantly. This effect can be reduced by the above construction.

As described above, in the zoom lens barrel assembly of the presentinvention, the opening/closing of the barriers 92 and 93 are performedby the slip motions of the third outer barrel 30, the second outerbarrel 23 and the relative movement of the fourth outer barrel 31 alongthe optical axis. In the zoom lens barrel assembly of the presentembodiment, the movement of the barrier drive ring 91 for closing andopening the barriers 92 and 93 is caused by two actions, namely, thestroke action of the fourth outer barrel 31 that takes place as thebarrel assembly shifts between the retracted position and the wide-angleextremity position, and the slip action of the third outer barrel 30 andthe second outer barrel 23 that takes place in the respective slipsections between the retracted position and the wide-angle extremityposition. Accordingly to this construction, the long stroke length ofthe fourth outer barrel 31 is utilized.

Referring to FIG. 28A, a part of the female helicoids 18 b of the firstlinear guide ring 18 is shown in an enlarged view in the vicinity of thehelicoid slip sections 18 b 1. In general, the first linear guide ring18 is made by injection-molding a plastic material. Accordingly, a moldis machined via electrospark machining. During the electrosparkmachining process, however, corners, such as those of the helicoid slipsections 18 b 1, are rounded (indicated by R in FIG. 28B). If thecorners of the helicoid slip sections 18 b 1 are rounded, the length ofeach thrust surface 18 b 2 of the helicoid slip section 18 b 1 along thecircumference of the barrel is reduced as well as the contact area withthe male helicoid 21 a. As a result, the surfaces interfere with themale helicoids 21 a. Furthermore, if the corners of the helicoid slipsections 18 b 1 are rounded, the thrust surfaces 18 b 2 can no longersupport the male helicoid 21 a against the thrust force thereof withsufficient stability.

However, in the present embodiment, a circumferential groove 18 e isformed along each of the front and the rear thrust surfaces 18 b 2 ofthe helicoid slip section 18 b 1, the surfaces being spaced apart fromeach other in the optical axis direction. As shown in FIG. 28C, thisconstruction eliminates the problem of rounded corners. Thecircumferential groove 18 e is formed to be wide enough (in the opticalaxis direction) to eliminate the rounded corners. Preferably, the widthis substantially the same as the radius of curvature of the roundedcorner that would otherwise be formed by electrospark machining.

In one embodiment, a circumferential groove 25 e similar to thecircumferential groove 18 e of the first linear guide ring 18 is formedalong each of the front and the rear thrust surfaces 25 b 2 of each ofthe helicoid-slip section 25 b 1 of the second linear guide ring 25.

When the male helicoids 21 a proceed from the helicoid slip sections 18b 1 into the female helicoids 18 b, if the second helicoid ring 21 andthe first linear guide ring 18 are not coaxially aligned or inclinedwith respect to each other, the end surfaces of the male helicoids 21 amay catch on the thrust surfaces 18 b 2, preventing the male helicoids21 a from proceeding into the female helicoids 18 b. In order to preventsuch a problem, an embodiment of the present invention includes flanges(eccentricity-preventing members) 18 f and 25 f to eliminateeccentricity. The flanges 18 f and 25 f are formed on the innerperipheries of the first linear guide ring 18 and the second linearguide ring 25, respectively, near the rear ends of the respective guiderings (see FIGS. 18A and 18B). The radial flanges 18 f and 25 f slidablyengage with, and close the end of, the second helicoid ring 21 and thethird outer barrel 30, respectively, when the second helicoid ring 21and the third outer barrel 30 are retreated to their respectiveretracted positions (see FIG. 29). In this state, the second helicoidring 21 and the third outer barrel 30 rotate through the slip sectionswhile sliding against the flanges 18 f and 25 f, respectively. In thismanner, backlash between the second helicoid ring 21 and the third outerbarrel 30 is prevented even when the rings are moving through the slipsections.

With this construction, the radial positions of the male helicoids 21 aand 30 a are restricted by the flanges 18 f and 25 f, and as a result,the male helicoids 21 a and 30 a can proceed from the respectivehelicoid slip sections 18 b 1 and 25 b 1 into the respective femalehelicoids 18 b and 25 b in a smooth and reliable manner. Once the malehelicoids 21 a and 30 a engage with the respective female helicoids 18 band 25 b, the helicoid mechanism causes the second helicoid ring 21 andthe third outer barrel 30 to advance or retreat between the wide-angleextremity position (FIG. 30) and the telephoto extremity position whilerotating.

Although in this embodiment, the flanges 18 f and 25 f are provided onthe inner peripheries of the first linear guide ring 18 and the secondlinear guide ring 25, respectively, similar structures with functionssimilar to the flanges 18 f and 25 f, such as projections, may beprovided on the inner peripheries of the second helicoid ring 21 and thethird outer barrel 31. An alternative construction is possible whereinthe bottom of the helicoid slip regions 18 b 1 (25 b 1) can be graduallyraised so that the helicoid slip regions 18 b 1 (25 b 1) have a largestdepth at a boundary region 18 b 3 (25 b 3) and have a smallest depth ata slip boundary region 18 b 4 (25 b 4), as shown in FIG. 28C.

In this embodiment, at least one of the lens barrels except for thefrontmost one is connected to the adjacent lens barrel through ahelicoid structure, and at least part of the helicoid that the lensbarrel follows as the lens barrel assembly moves from a retractedposition to a minimally extended photographing position is formed as aslip section that allows the lens barrel to rotate without advancing orretracting. Thus, this construction not only ensures rigidity of thelens barrel assembly, but also achieves sufficient displacement betweenthe frontmost lens barrel and other lens barrels for providing asufficient stroke to open and close the barrier via a predeterminedrotation angle.

According to this embodiment, the multi-stage-extension zoom lens barrelassembly includes a helicoid structure which causes two connected lensbarrels to rotate and move along the optical axis relative to each otheras the zoom lens barrel assembly moves between a retracted position anda minimally extended photographing position, and the helicoid structureincludes a helicoid slip region that causes the two barrels torelatively rotate without relatively moving along the optical axis.Also, the helicoid slip region includes a female helicoid formed on oneof the two barrels to be connected and a male helicoid formed on theother of the two barrels, and the female helicoid includes a helicoidslip region that permits rotation of the male helicoid when the twobarrels are in the retracted position. A circumferential groove isformed along each of thrust surfaces of the helicoid slip region.Accordingly, components of the lens barrels that have the helicoid slipregion can be formed with high precision and at a lower cost.

According to the above description, the zoom lens barrel assembly of thepresent invention, in which telescopic movement of the lens barrels isrestricted by a stopper member engaging an end tooth of gear teeth onthe helicoid ring, has a simple stopper construction for the lensbarrels with fewer components. This construction also facilitatesdisassembly of the zoom lens barrel assembly since the helicoid ring canbe rotated past the normal operative position to the disassemblyposition by simply removing the stopper member.

Furthermore, the interference-preventing member prevents the flexibleprinted circuit board from interfering with the gear teeth of thehelicoid ring even when the FPC is placed close to the path of the endtooth of the gear teeth of the helicoid ring.

Obvious changes may be made in the specific embodiments of the presentinvention described herein, such modifications being within the spiritand scope of the invention claimed. It is indicated that all mattercontained herein is illustrative and does not limit the scope of thepresent invention.

What is claimed is:
 1. A zoom lens barrel assembly, comprising: aplurality of lens barrels including a rearmost lens barrel, secured to acamera body, and a frontmost lens barrel; wherein at least two adjacentlens barrels, of said plurality of lens barrels arranged between thecamera body and the frontmost lens barrel, are connected to each othervia a helicoid structure; wherein the frontmost lens barrel and a firstadjacent lens barrel are connected to each other via a cam structure;wherein said helicoid structure allows said at least two adjacent lensbarrels to rotate and move in an optical axis direction relative to eachother while the zoom lens barrel assembly moves from a retractedposition to a minimally extended position for a photographing operation;and wherein at least a portion of the helicoid structure includes a slipregion which allows said at least two adjacent lens barrels to rotatewithout relatively moving along the optical axis.
 2. The zoom lensbarrel assembly according to claim 1, wherein a barrier mechanism isprovided on the frontmost lens barrel, said barrier mechanism beingopened and closed via movement of the frontmost lens barrel in theoptical axis direction as the zoom lens barrel assembly moves betweenthe retracted position and said minimally extended position, and byrelative rotation of said at least two adjacent lens barrels via theslip region.
 3. The zoom lens barrel assembly according to claim 1,wherein said first adjacent lens barrel connected to the frontmost lensbarrel via said cam structure is connected to a second adjacent lensbarrel via a second helicoid structure which causes the connected saidfirst and second adjacent lens barrels to rotate and move along theoptical axis relative to each other as the zoom lens barrel assemblymoves from the retracted position to the minimally extended position,said second helicoid structure also including a slip region which allowssaid first adjacent lens barrel and said second adjacent lens barrel torotate without relatively moving along the optical axis.
 4. Afour-stage-extension zoom lens barrel, comprising: a first barrelconnected to a fixed barrel secured to a camera body, said first barrelbeing movable so as to retreat and advance relative to the fixed barrel;a second barrel connected to the first barrel; a third barrel connectedto the second barrel; a frontmost fourth barrel connected to the thirdbarrel; wherein said first, second, and third barrels are eachsupported, and are movable in an optical axis direction, via a helicoidstructure; wherein said frontmost fourth barrel and said third barrelare connected to each other by a cam structure so as to be movable in anoptical axis direction; wherein a barrier mechanism is provided on saidfrontmost fourth barrel; wherein the helicoid structures for moving thesecond barrel and the third barrel in the optical axis direction eachallow the second and the third barrels to rotate and relatively move inthe optical axis direction as the zoom lens barrel moves between aretracted position and a minimally extended position for a photographingoperation, each said helicoid structure having a slip region whichallows the second and third barrels to rotate without relatively movingin the optical axis direction; and wherein said barrier mechanism isopened and closed by a relative movement of said third barrel and saidfrontmost fourth barrel in the optical axis direction as said slipsections allow the second and the third barrels to rotate.
 5. Thefour-stage-extension zoom lens barrel according to claim 4, wherein thefourth barrel is connected to the third barrel via the cam structure sothat the fourth barrel moves in the optical axis direction relative tothe third barrel without rotating, and the barrier mechanism is openedand closed by said relative movement of the third barrel and the fourthbarrel in the optical axis direction in the slip section of the thirdbarrel.
 6. The four-stage-extension zoom lens barrel according to claim4, wherein the slip section of the helicoid structure of the secondbarrel has a different slip angle than the slip section of the helicoidstructure of the third barrel.
 7. The four-stage-extension zoom lensbarrel according to claim 4, wherein said helicoid structure having theslip section includes a female helicoid formed on one of two adjacentbarrels of said first through third barrels and a male helicoid formedon the other of said two adjacent barrels, and wherein the femalehelicoid includes a helicoid slip region that permits rotation of themale helicoid when said two adjacent barrels are in a retractedposition.
 8. A zoom lens barrel assembly, comprising: a plurality oflens barrels including a rearmost lens barrel secured to a camera body,and a frontmost lens barrel; wherein the frontmost lens barrel and afirst adjacent lens barrel are connected to each other via a camstructure; wherein said first adjacent lens barrel is connected to asecond adjacent lens barrel via a helicoid structure so that said firstand second adjacent lens barrels relatively rotate and relatively movein the optical axis direction as the zoom lens barrel assembly movesbetween a retracted position and a minimally extended position for aphotographing operation, said helicoid structure including a helicoidslip region which allows said first and second adjacent lens barrels torelatively rotate without relatively moving along the optical axis;wherein said helicoid structure having the helicoid slip region includesa female helicoid formed on one of said first and second adjacent lensbarrels and a male helicoid formed on the other of said first and secondadjacent lens barrels; wherein said female helicoid includes a helicoidslip region which permits rotation of the male helicoid when said firstand second adjacent lens barrels are in the retracted position; andwherein a circumferential groove is formed along each of opposing thrustsurfaces of the helicoid slip region.
 9. The zoom lens barrel assemblyaccording to claim 8, wherein said helicoid structure having saidhelicoid slip region and said circumferential groove constitute ahelicoid ring, said helicoid ring being formed by injection-molding aplastic material into a mold.
 10. A zoom lens barrel assembly,comprising: a pair of lens barrels connected to each other via ahelicoid structure, said helicoid structure including a helicoid slipregion which allows said pair of the lens barrels to relatively rotatewithout relatively moving along the optical axis; wherein said helicoidstructure having the helicoid slip region includes a female helicoidformed on one of said pair of lens barrels and a male helicoid formed onthe other of said pair of lens barrels; wherein said female helicoidincludes the helicoid slip region which allows rotation of the malehelicoid when said pair of lens barrels are in a predetermined position;and wherein a circumferential groove is formed along each of opposingthrust surfaces of the helicoid slip region of the female helicoid. 11.A zoom lens barrel assembly, comprising: a plurality of lens barrels, atleast two lens barrels of said plurality of lens barrels including ahelicoid structure for allowing one lens barrel of said at least twolens barrels to rotate and extend and retreat as the zoom lens barrelassembly moves from a retracted position to a minimally extendedposition for a photographing operation; wherein said helicoid structureincludes a helicoid slip section for allowing said one lens barrel torotate without relatively moving along the optical axis, said helicoidstructure including a female helicoid formed on one of said at least twolens barrels and a male helicoid formed on the other of said at leasttwo lens barrels, the male and the female helicoids including a helicoidslip region that allows said at least two lens barrels to rotate andprevents said at least two lens barrels from moving along the opticalaxis when one of said at least two lens barrels is retracted into theother; and an eccentricity-preventing member provided on said at leasttwo lens barrels for allowing said at least two lens barrels to slidablyand closely engage with each other so as to slide circumferentially andslide in the optical axis direction, said eccentricity-preventing memberguiding rotation of said at least two lens barrels via said helicoidslip section when one of said at least two lens barrels is retreated andslightly advanced with respect to the other of said at least two lensbarrels.
 12. The zoom lens barrel assembly according to claim 11,wherein said eccentricity-preventing member is formed as a flange whichextends circumferentially and projects radially inward from an innerperiphery of one of said at least two lens barrels which is providedoutside of the other of said at least two lens barrels, said flangebeing formed in the vicinity of said helicoid slip section and slidablyplaced over an outer periphery of an inner lens barrel of said at leasttwo lens barrels.
 13. The zoom lens barrel assembly according to claim11, wherein each of said plurality of lens barrels arranged between acamera body and a frontmost lens barrel is connected via the helicoidstructure, said front most lens barrel and a first adjacent lens barrelbeing connected to each other via a cam structure, and wherein saidfirst adjacent lens barrel and a second adjacent lens barrel connectedthereto constitute said at least two lens barrels.
 14. The zoom lensbarrel assembly according to claim 11, wherein a barrier mechanism ismounted on said frontmost lens barrel, the barrier mechanism beingopened and closed by relative movement of said frontmost lens barrel andsaid first adjacent lens barrel in the optical axis direction as thezoom lens barrel assembly moves from the retracted position to theminimally extended position for a photographing operation.